As with speech data files, HTK not only defines its own format for label files but also supports a number of external formats. Defining an external format is similar to the case for speech data files except that the relevant configuration variables for specifying a format other than HTK are called SOURCELABEL and TARGETLABEL. The source label format can also be specified using the -G command line option. As with using the -F command line option for speech data files, the -G option overrides any setting of SOURCELABEL